Problem: If $7a + 6b = -8$ and $4x + 8y = -6$, what is $-8x + 49a - 16y + 42b$ ?
$= 49a + 42b - 8x - 16y$ $= (7) \cdot (7a + 6b) + (-2) \cdot (4x + 8y)$ $= (7) \cdot (-8) + (-2) \cdot (-6)$ $= -56 + 12$ $= -44$